The present invention relates to a video tape recorder (VTR) for recording and reproducing video signals and, more specifically, to a digital/analog compatible VTR which is capable of dealing with both digital and analog video signals.
Current domestic VTRs are analog VTRs using xc2xd in. oxide tapes for recording analog TV signals.
Digital broadcasting systems have been developed as TV broadcasting systems of the next generation and efforts have been made for the development of practical transmission systems, for digital transmission using satellites, ground waves and cables. For example, there is in the U.S.A. an ATV (Advanced Television) system using a bandwidth of 6 MHz, which is used for current TV broadcasting, that processes wide-band video signals of high definition (hereinafter referred to as xe2x80x9cHigh Definition (HD) video signalsxe2x80x9d) higher than those of video signals of the current NTSC system and the PAL system (hereinafter referred to as xe2x80x9cStandard Definitionxe2x80x9d (SD) video signals) into compressed and coded digital video signals. The MPEG (Moving Picture Experts Group) system is a known SD video signal system. Refer to Terebijon Gakkai-shi, Vol. 47, No. 4, pp. 486-503 (1993) for the further details concerning digital broadcasting systems.
It is expected that those digital broadcasting systems will be employed together with analog TV broadcasting systems in the near future. Accordingly, for practical use of digital broadcasting or digital transmission, a practical development is expected to be made of VTRs of the digital recording system type which are capable of recording digital signals utilizing the feature of digital transmission in which signals are not deteriorated by transmission systems. However, digital VTRs have been used practically only in special fields, such as in the business field because the information content of digital video signals is greater than that of analog video signals. Recent advancement in image-compressing techniques represented by the MPEG system has made possible the miniaturization of digital equipments and the extended use of digital techniques for domestic equipments. Refer to Terebijon Gakkai-shi, Vol. 47, No. 6, pp. 814-825 (1993) for further details concerning digital recording techniques. Domestic digital VTRs having an original recording format have been developed. However, most users keep analog-recorded tapes collected as property, and there are problems in digital VTRs in price, floor space necessary for installation and the use of the collected analog-recorded tapes.
Accordingly, VTRs capable of recording and reproducing signals in both the analog system and the digital system have been desired. However, it is expected that the following problems reside in VTRs capable of dealing with both analog and digital systems. Firstly, since analog recording and digital recording use different input sources, respectively, the user needs to select the recording system and the input source and to confirm the coincidence of the selected recording system and input source, which requires troublesome operations for recording and increases the possibility of erroneous operations. Secondly, there are problems in using tape cassettes of the same shape, including those containing tapes on which signals are recorded by the analog system and those on which signals are recorded by the digital system. For example, when recording signals on a tape carrying recorded signals by the current analog VTR in a continuous mode or an overwrite mode, the contents of the tape must be reproduced tentatively for confirmation. However, when tapes of both the analog system and the digital system are used together, the user is unable to recognize pictures recorded by either system unless the reproducing system coincides with the selected recording system and the input source; consequently, there is the possibility that the user misunderstands that no signal is recorded on the tape and overwrites new signals on the tape, thereby erasing the previously-recorded signal mistakenly. In addition, when an increasing number of recorded tapes of the digital system are used, there is a problem that the user is unable to recognize signals recorded on the tape of the digital system with the current analog VTRs, resulting in erasing of the previously-recorded signal mistakenly.
Most current analog VTRs are provided with an audio head independently of a video head on a rotary drum to record FM signals in the depth of a magnetic tape. Therefore, it is disadvantageous from the point of view of cost and productivity to provide on a rotary drum a magnetic head specially for digital recording and reproducing and a proposal is made for the use of an audio head also for digital recording. However, when an FM audio head is used also as a digital head, an audio signal processing circuit is actuated, which processes digital signals for audio processing when reproducing the digital signals and supplies the audio-processed digital signals to a loudspeaker. Then, the loudspeaker generates abnormal sounds and, in the worst case, the loudspeaker might be destroyed. Although the conventional VTR has an automatic tracking control function to provide reproduced outputs on the highest level, the VTR needs a new automatic tracking control function for operation in a digital recording mode. When the VTR is provided with a decoding circuit for expanding compressed and coded digital video signals and converting the expanded digital video signals into composite video signals, the circuits need to be changed according to mode identifying information.
Accordingly, it is a first object of the present invention to provide a digital/analog compatible VTR which is capable of recording and reproducing both analog signals and digital signals, having an automatic digital/analog mode identifying function, and which is capable of being easily operated for recording and reproducing operations and of preventing erroneous operations, such as an erroneous erasing operation.
A second object of the present invention is to provide the aforesaid digital/analog compatible VTR with an optimum automatic tracking control function.
With the foregoing objects in view, the present invention provides a digital/analog compatible VTR that identifies the type of tape cassette by an identification hole formed in the tape cassette, determines tape speed for recording from the ratio between the frequency of a control signal and the rotational velocity of a capstan motor for feeding tapes, determines whether or not there is a digital recording signal through the synchronous detection of reproduced signals, and selects either a recording mode or a reproducing mode according to these determinations. For example, when carrying out a recording operation, the type of the tape cassette is identified, and the digital/analog compatible VTR automatically selects a recording circuit and an input source to give priority to digital recording when a digital recording cassette is loaded into the VTR. Therefore, the user need not perform any operation for setting input signals, and only digital signals are recorded on tapes for digital recording to facilitate tape management. When a reproducing instruction is given, the digital/analog compatible VTR selects a reproducing mode for the most probable recording system according to the result of detection of the type of tape cassette, for example, the digital reproducing mode when a tape cassette containing a tape on which digital video signals are recorded is loaded into the digital/analog compatible VTR, to curtail the time necessary for starting the reproducing operation after the reproducing instruction has been given thereto.
The digital/analog compatible VTR of the present invention carries out a reproducing operation prior to a recording operation, and identifies the type of loaded tape cassette by the existence or absence of the digital tape cassette identification hole, or detects a signal indicating the digital system through the determination of tape speed for recording on the basis of the ratio between the frequency of a control signal and the rotating velocity of a capstan motor. Consequently, erroneous erasing by overwriting can be prevented by inhibiting the recording operation when it is determined that digital signals are recorded on the tape.
Furthermore, the digital/analog compatible VTR achieves automatic mode identification through the detection of the frequency of reproduced signals provided by an FM-audio/digital recording head for both FM audio signal recording and digital signal recording, automatically switches between the respective output signals of an output level detecting circuit for detecting the level of the output signals of an analog video signal recording head and the FM-audio/digital recording head, and executes an automatic tracking control operation so that the output signals are on the highest level in each mode. When processing digital signals, the identifying performance can be further enhanced through the identification of a phase-locked state by a phase-locked loop (PLL). A high-performance tracking state can be secured in both an analog mode and a digital mode by switching the path of the automatic tracking control to an analog signal processing side or a digital signal processing side according to the result of mode identification.